Interesting concept wind energy system - but will it work?

Steven Lake
Steven Lake Solar Expert Posts: 402 ✭✭
in General Solar Power Topics #1
Ok, I'm back with another neat invention for you to consider. Or at least this one will be a real unit in time, as it's only a concept model at this point. Anyhow, I got to talking with some friends of mine about renewable energy recently, and along the way we somehow got on the subject of using a windmill as a green form of air compressor. Yes, it sounds nuts, but hey, anything's possible if you try hard enough. ;)

Anyhow, my comment about a windmill powered compressor was done more as a tongue in check comment. However, since a number of those friends I talked with are engineers, they took my jovial comment as a challenge. Fast forward one week and they bring me this idea for a wind powered renewable energy system for completely off grid living. I'm personally not sure if it'll work, but the idea sounds really interesting. Anyhow, here's what they came up with. Take an old style mechanical windmill (like the kind used to pump water on farms) and use it to turn a two stage high pressure compressor (via a gearbox or something. I'm not totally sure) and charge an air tank. That air is then used to run an air powered motor which drives a dc generator which in turn charges a bank of super capacitors which in turn connect to an inverter which powers whatever is attached to it.

To me the idea sounds completely impractical, and a compete waste of time. But as with any engineering geek, a challenge like this sounds completely irresistible. Or at least it is with these four. Seesh. Anywho, I thought I'd throw it your way and see what you thought about it. Again, this is just one of those crazy "let's prove that it can be done" engineering projects, and not something that's intended on being a practical solution to anything (sorta like the solar powered water tank fueled hydro concept I posted about before). But in the end, who knows. Anything is possible. :)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Interesting concept wind energy system - but will it work?

    Go back in time about 100 years: it's been done. At least with low pressure compression.
    It's about as efficient as a government agency.
    You can't cheat physics. In order to get high pressure air you have to come up with the raw power from somewhere. Wind over time? Ever-so inefficient for generating an appreciable volume of highly-pressurized air. For one thing compressing the air will turn much of the harvested energy into heat which will radiate off without ever doing any work.Then you're going to let that air out in a whoosh! to spin a turbine (or worse, piston motor)? More efficiency losses. Air is far less dense than steam or water, so the conversion losses would be large at every stage.

    Better to use the windmill to lift water up a hill and allow it to flow back down through a water turbine: the windmill pump could keep the reservoir filled and the weight of the water could be released as needed to provide power.

    If these guys had been in my science class they'd have been looking at attending Summer school. :roll:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Interesting concept wind energy system - but will it work?

    By the way, using a windmill compressor with the air dumped to the bottom of a well--then using the air bubbles to carry water to the surface is also done.

    Airlift Technologies
    CI Solar wind pumping

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #4
    Re: Interesting concept wind energy system - but will it work?

    Cariboocoot: Yeah, that's kinda what I came to as well (IE, it wouldn't work), but I figured to get a 2nd opinion since I'm only a "silly programmer" and not an engineer. lol. OH well, I say, let them have their fun. They're rather OCD about "impossible" projects like this. Then again, they've taken on a few other odd ideas like this and actually found ways to make them work, believe it or not. Thus I'm content to let them at least give it a try. The worst it does is keep them out of my hair for a few weeks or so. ;)

    BTW, your idea to use the windmill to pump the water uphill does give me an interesting idea, as I remember posting in another forum thread about someone doing that exact same idea with wind pumped hydro. (or was it solar pumped? I can't remember) Maybe I'll suggest having them repeat the experiment once all the air goes out of this one. haha.

    BB: That's neat! Thanks for the info! :D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Interesting concept wind energy system - but will it work?

    I didn't say it wouldn't work, just that it would be very inefficient. Probably to the point of impracticality. Like one day's pumping for fifteen minutes of power. :roll:
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #6
    Re: Interesting concept wind energy system - but will it work?

    All jokeing aside, I heard about this Amish blacksmith that uses a windmill to pressureize a big propane tank to power his air tools. Most of them aren,t allowed to use electric but go to a lot of problems to have power tool l that either have gas engines, air powered or hydralic motors. He has one of those old style windmills with an air compresser. For non windy days he has a gearbox that he hooks his horse to that goes around it in a circle. I hadn,t seen it but a person that took some Amish out to eastern pa area told me about it. Went to an Amish cabinet shop that had all power tools that any other cabinet shop would have. He had hydralic motors on everything and a small diesel to run the hydralic pump. They also make use of line shaft. In his barn he has a diesel engine connected to a line shaft. Runs his engine for a vacume pump at milking time to run his milking machines. Also has an air compresser he connects to a large propane tank to pressurize it with air for any appliances he might have in the house and his air tools. They have the DAYTON floor model fans with a a single piston powered air pump to run the fan. I was amazed how well it works. These air motors kind of remind you of a steam engine the way it runs. :Dsolarvic:D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Interesting concept wind energy system - but will it work?

    They are very much like a steam engine: exactly the same principle. Except that steam has a much higher density and will transfer more power for the equivalent pressure. And it's easier to get pressure from a fired boiler than from a wind-driven pump. Although sometimes you can get too much pressure. Ka-boom! :cry:

    Most air tools run around 90 psi with 5-6 cfm. Some require less pressure and more flow, others more pressure and less flow. Constant running is what will get you there; a relatively small compressor can keep up if you stop ever now and then and let the air pressure build in the tank. The larger the tank, the less often the compressor has to come on (or in the case of the windmill, the easier it will stay ahead). Just like with water systems.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #8
    Re: Interesting concept wind energy system - but will it work?

    Very true. I think that may have been the idea behind putting the super capacitors on there. (the ones they use are the HUGE 48v kind you'd see at a power station. They get them surplus from ma-electric for cheap) Since a capacitor (at least from my understanding) is 95% efficient on charge storage vs 70% for batteries, it's the more logical choice. That way you would be able to run the generator on the air tank for a short time, long enough to charge the capacitor, then run off it until it needed to be charged again. Meanwhile the windmill could be working to build up the required pressure and volume to run the motor.

    Again, I'm going on what I understand, so take my thoughts with a grain of salt. ;)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: Interesting concept wind energy system - but will it work?
    Steven Lake wrote: »
    Very true. I think that may have been the idea behind putting the super capacitors on there. (the ones they use are the HUGE 48v kind you'd see at a power station. They get them surplus from ma-electric for cheap) Since a capacitor (at least from my understanding) is 95% efficient on charge storage vs 70% for batteries, it's the more logical choice. That way you would be able to run the generator on the air tank for a short time, long enough to charge the capacitor, then run off it until it needed to be charged again. Meanwhile the windmill could be working to build up the required pressure and volume to run the motor.

    Again, I'm going on what I understand, so take my thoughts with a grain of salt. ;)
    I am not a power engineer, but I would hazard a guess that those big capacitors are meant for waveform smoothing, not for long term energy storage; I wonder how many Ah you can get out of one. Also, it's been many years since school, but IIRC, unlike a battery, a capacitor's voltage decreases linearly as it discharges. If that is correct, a 48V battery at 50% SOC still produces close to 48V, but a 48V capacitor at 50% SOC is at 24V.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Interesting concept wind energy system - but will it work?

    The super caps are not a solution either... Besides being very large for small amounts of energy storage... Some numbers:
    • 1/5th the amount of energy storage per kg vs lithium ion batteries
    • 10x the cost per kWH of storage vs lithium ion batteries
    • (this vendor) the operation voltage is [FONT=Arial, Helvetica, sans-serif]2.3 to 2.75V for supercap[/FONT]
    • [FONT=Arial, Helvetica, sans-serif]wider operating temperature range vs L-I batteries[/FONT]
    • [FONT=Arial, Helvetica, sans-serif]Cycle life of 1,000,000 cycles / 30,000 Hours[/FONT]
    Note that the energy storage of a capacitor goes with the square of the voltage--So for optimum power storage/usage, you would need a MPPT / Switching Power Supply to up/down convert the variable voltage of the capacitor to the (typically) fixed voltage of the charging/load circuits. So a S.C. at 1/2 voltage only has 1/4 the energy vs fully charged.

    Cycle Life at 1 million cycles sounds great, but the the applications for capacitors is ~10 seconds vs 10's of minutes to hours/days usage for the typical battery application.

    Apparently the "on time" life is ~30,000 Hours (at least for one supercap) -- which works out to less than a 4 year life for long term energy storage usage.

    In the end, I think that supercaps have a very limited usage/application range. And for off-grid emergency power usage--what you see now for battery technology is what you are going to use for the next decade or two (if not longer). Other than tinkering at the edges (higher charge/discharge rates, life time, safety issues), I don't think you are going to see a 2-10x "improvement" storage capacity (kWH per lb/per cu.ft.) or a Mr. Fusion in our lifetime.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #11
    Re: Interesting concept wind energy system - but will it work?

    lol. Sounds like the guys are going to have a major case of egg on their face if they try this, based on what you guys are pointing out. Oh well, a little failure once in a while is good for the engineering types who think they can make anything work. ;)

    On a small side note, if they went with a closed loop wind pumped hydro setup instead, it might work a bit more efficiently, but even that would have way too many losses to be practical. I guess, if you really think about it, renewable energy is all about getting the most output with the least amount of loss in the most practical manner available.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #12
    Re: Interesting concept wind energy system - but will it work?

    HAHAHAHAHA! Leave it to a Bolivian engineer to kill the idea where it stands. Apparently the guys were discussing their plans while at work and one of the other engineers in the office, a Bolivian who was up here as an advisor for one of the company's projects, more or less told the guys that their "stored energy via compressed air" idea was stupid. Well, he apparently used some more *colorful* words than that, but that was the gist of it. lol. So as of this point, the idea is dead. But not to be completely defeated, they're still going to strap a DC generator to the drive shaft and try to milk at least a little power out of it. (*rolls eyes*)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Interesting concept wind energy system - but will it work?
    Steven Lake wrote: »
    But not to be completely defeated, they're still going to strap a DC generator to the drive shaft and try to milk at least a little power out of it. (*rolls eyes*)

    Unless they strap an internal combustion engine to the drive shaft they're still going to come up short. :roll:
    You never get more power out than you put in. In fact you usually don't even come close to the amount put in.

    One of the reasons we keep using the horrible fossil fuels: lots of energy jammed into a little space by 65 million years of compression.

    You sure those guys are engineers? They sound more like bureaucrats: get funding and keep spending it even though there's no chance the project will ever succeed.

    (This was one of the big differences between Edison and Tesla: the former just kept trying things until he found what would work, the latter determined what would work before he tried it.)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #14
    Re: Interesting concept wind energy system - but will it work?
    Cariboocoot wrote: »
    Unless they strap an internal combustion engine to the drive shaft they're still going to come up short. :roll:
    You never get more power out than you put in. In fact you usually don't even come close to the amount put in.

    The First Law of Thermodynamics: Everything goes to, uh, fecal matter.

    The Second Law of Thermodynamics: The best you can do is break even.

    The Third Law of Thermodynamics: You can't break even.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #15
    Re: Interesting concept wind energy system - but will it work?

    Note, there is/was a compressed air storage system. The compressed air was supplied to to the intake of a natural gas peaker turbine. Saves the losses from the initial compressor turbine and increases turban output during peak load demands.

    I think the air was stored in an old salt mine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #16
    Re: Interesting concept wind energy system - but will it work?

    Well, the windmill they're using is one of the newer kind with a gearbox at the top which takes the rotation of the fan shaft (forgive me if I'm naming these wrong, but I'm describing them the best I can) and converts it 1:1 to a vertical shaft which extends from the top down to the base. Normally that's connected into a rotary pump. But they were intending on connecting it to an air compressor which would create stored energy by compressing air and storing it in a really big tank, then drawing off that tank whenever power was needed. All they're doing now is taking out the middle man (ie, removing the compressor, air motor and the tank) and running the dc motor directly off the vertical drive shaft. I don't know if it'll be a 1:1 conversion, but it'll likely have to be put into a gearbox that steps up the output RPM's enough to make practical use of the wind power.

    Anyhow, that's the theory. What the three stooges engineering corporation ends up doing though will likely be something different. lol.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #17
    Re: Interesting concept wind energy system - but will it work?

    Boy, you put these guys on a mission and they won't stop till they get a working system, even if it's not possible. lol. Alright, here's what they've done so far, and oddly, it works. Don't ask me how as I can't explain it, but it works.

    First, they hooked up the main driveshaft from the windmill on top (the fan connects to a 1:1 gearbox which transfers the power down a long metal driveshaft to the base) to a variable speed gearbox at the bottom. From what they describe of this thing, it's designed to, through some oddball manual process, keep the output RPM's at the exact same rate, no matter what the input shaft is spinning at. (I'm gonna guess that they're using one of these: http://en.wikipedia.org/wiki/Continuously_variable_transmission, or at the very least, something similar in design)

    Anyhow, the gearbox (CVT, or whatever it is) connects to an AC generator (thus eliminating the need for capacitors and inverters in the system, which they found was a big fail because it caused too much loss) which in turn powers the test load. Now here's something interesting about the design. Since the guys were bound and determined to make a pressurized air backup system (have I mentioned how stubborn these guys are? lol) they have the system setup to take the excess electricity produced by the generator and use it to run a high pressure compressor which fills a couple of huge high pressure air tanks until they're at capacity. When they're full the gearbox spins down the generator to match demand.

    Now, should demand exceed available production potential, air is taken from the tanks and used to run an air powered motor which turns a second AC generator that picks up the slack in the system. The only downside to the design so far is that it takes up a lot of space (something like a thousand square feet, most of which is consumed by the air tanks), it only has a 24 hour reserve capacity and the backup generator can't provide over a given wattage (3000w if I remember right. But then again, the main is 3000w too) so if you hit into some heavy usage, you're kinda screwed as it'll kick out the entire system.

    Anyhow, that's what my mad scientist/engineer friends have come up with. Overall the system seems to be working so far (cross your fingers) but it has a lot of drawbacks, and probably is only pulling 50% efficiency at best, but amazingly enough, it does work. But again, they only got it working a few days ago, so there's no long term data with it yet. I suspect that if allowed to run over the long haul we'll see enough fails that it'll make the design completely impractical. Well, assuming it's size and clunkiness hasn't already done that. ;)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
    Re: Interesting concept wind energy system - but will it work?

    Never said it wouldn't work. Just about as efficient as a government agency. :roll:
    Windmills work best the old fashioned way: direct use of the available mechanical power. The "old ones" http://kaleidopsyche.deviantart.com/art/Alternate-Energy-135595808 turned the mechanical power from a horizontal shaft to a vertical one at the head (allows easy pivoting) and that shaft ran down into the well and terminated in a screw-type pump. Enough wind to turn the blades at whatever speed became some lift of water even if at a small rate of flow (zero pressure).

    Now if your genius engineers would take a course in physics and one in accounting they'd see their time would be better spent watching paint dry.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #19
    Re: Interesting concept wind energy system - but will it work?
    Cariboocoot wrote: »
    Never said it wouldn't work. Just about as efficient as a government agency. :roll:
    Windmills work best the old fashioned way: direct use of the available mechanical power. The "old ones" http://kaleidopsyche.deviantart.com/art/Alternate-Energy-135595808 turned the mechanical power from a horizontal shaft to a vertical one at the head (allows easy pivoting) and that shaft ran down into the well and terminated in a screw-type pump. Enough wind to turn the blades at whatever speed became some lift of water even if at a small rate of flow (zero pressure).

    Now if your genius engineers would take a course in physics and one in accounting they'd see their time would be better spent watching paint dry.
    I wouldn't be so quick to judge. Sometimes if you start with a hare-brained idea and keep refining it by throwing away the parts that don't work toward the goal you end up with something worthwhile. Of course, what you end up with may not contain any vestiges of the original idea, but it's the process that yields the results and the original idea may be irrelevant.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: Interesting concept wind energy system - but will it work?
    ggunn wrote: »
    I wouldn't be so quick to judge. Sometimes if you start with a hare-brained idea and keep refining it by throwing away the parts that don't work toward the goal you end up with something worthwhile. Of course, what you end up with may not contain any vestiges of the original idea, but it's the process that yields the results and the original idea may be irrelevant.

    The difference between Edison's methods and Tesla's methods.
    I'll go with Tesla. :roll:
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #21
    Re: Interesting concept wind energy system - but will it work?

    Oh, I agree with both of you. The idea may not be practical, but given that they went from a non-working idea to a working one (albeit overly bulky and highly inefficient) in such a short time is commendable in itself. In the end it'll probably get abandoned. But what they learn from it in the meantime should be quite interesting.

    On a side note, their use of compressed air as a storage medium for energy is only slightly different from what the big electrical companies do with "pumped storage". Ie, they use a physical medium (in this case, water, rather than air) in order to store power for later use when system demand requires it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: Interesting concept wind energy system - but will it work?
    Steven Lake wrote: »
    On a side note, their use of compressed air as a storage medium for energy is only slightly different from what the big electrical companies do with "pumped storage". Ie, they use a physical medium (in this case, water, rather than air) in order to store power for later use when system demand requires it.

    A very good point.
    And here's another: water is considerably denser than air.

    One of the reasons fossil fuels are efficient is because Mother Nature has already compressed the carbon, hydrogen, and oxygen into a very tight little package. So much so that even after using vast quantities of energy to extract and process the stuff you still have a net energy gain. Pity it's so nasty to burn.

    If only we could get solar cells to operate around 90% efficiency (and not cost 6 times what they do now) and get more efficient batteries that likewise do not cost an arm and a leg.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #23
    Re: Interesting concept wind energy system - but will it work?

    I agree. But I think in the meantime, what with the way battery technology is improving by leaps and bounds, they need to invent a battery that has the charging efficiency of a capacitor (or higher, like 95% efficiency if possible) with the long power curve of a battery. They've already gone the other way with batteries that have a very high discharge rate, so having the opposite with good efficiency would help to make up for the currently lesser efficiency of the solar cells by ensuring that more of the energy gets stored and less of it gets lost. That in and off itself would be a huge improvement.

    And on a further note, I've been researching charging systems for a while, and one I ran into is called "Radiant Energy Charging". Essentially the system doesn't provide a continuous current to the battery. It sends repeated high voltage charges (24-48v) in short, quick spikes to the battery. From everything I've seen, the batteries love it. Not only that, but they don't heat up or boil off like straight current charging does. It also seems to allow for a much faster charge rate too. The thing is, only one company sells it, and there's no open reviews of it, so I can't say one way or another how actually authentic it is. But if it's authentic, the ramifications alone are huge. :)
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